TECHNICAL REPORT

Bearing & Seal Technologies for Project

C. MUROTANI

In the industry-academy collaborative Eliica project to develop a high-performance electric vehicle, Koyo was responsible for developing and supplying bearings and seals for in-wheel motor drive systems. Koyo's supply of bearings and seals that can operate at the designed maximum vehicle speed of 400 km/h has contributed to the success of the Eliica project.

Key Words: electric automobile, environment, in-wheel motors, lithium-ion battery, Tokyo Motor Show

1. Introduction 2. Outline of Eliica Project Keio University and thirty-eight companies actively coping Although environmental concerns have given birth to strong with environmental problems teamed up to form an industry- public demand for the spread of electric vehicles, there so far academy collaborative organization for the development of a has been no vehicle having performance comparable to that of new-concept electric vehicle named the "Eliica." In September conventional internal combustion engine vehicles to satisfy 2004, the project successfully completed the first stage consumers' needs. prototypes, which achieved planned targets. Keio University previously carried out a project named the This project was publicized at the 37th Tokyo Motor Show "KAZ," to construct an eight-wheel electric vehicle applying in 2003. It was also featured in a NHK TV program in October specific designs for electric vehicles instead of modifying an 2004. Behind such success that has evoked enormous public existing vehicle, and Koyo provided bearing and seal interest, there were various contributions by participants in the technologies. Applying optimized element technology, vehicle project. Koyo, as one of them, undertook development of overall structural technologies specific to electric vehicles bearings and seals for the in-wheel drive system, as introduced were invented and employed to improve the vehicle hereunder. performance and function. As a result, the KAZ achieved good acceleration and sufficient compartment space that is unique for an electric vehicle. In addition the KAZ achieved good cornering performance, drivability on rough roads comparable to that of conventional internal combustion engine vehicles, and satisfactory mileage per charge. However, in order for an electric vehicle to be accepted in the market, it needs to be sufficiently safe, high-performing, and comfortable. Furthermore, it is also necessary to convince society that an electric vehicle is something realistic not only by establishing necessary technologies but also by proving its feasibility for mass-production. In an attempt to achieve this, the Eliica project was launched with the objective of creating an electric vehicle that would, in the long term, be used by society, even if produced in small lots. The Eliica first stage prototype was built for the purpose of applying such core technologies as lithium-ion batteries, in-wheel motors, component built-in frames and tandem-wheel suspension, which were developed in the KAZ for an ordinary passenger vehicle. Fig. 1 Appearance of "Eliica" first-stage prototypes1)

Koyo Engineering Journal English Edition No.168E (2005) 35 −Bearing & Seal Technologies for Electric Vehicle Eliica Project− q In-wheel motor q Environmental friendliness This is a drive unit comprised of an , · No gas emissions reduction gears, a wheel bearing and a braking system, all of · Quiet operation which are housed together inside the wheel and enable · 1/3 or less energy consumption than a gasoline engine minimized energy loss during operation, simplify the vehicle vehicle, supposing electricity generated from petroleum structure, and expand passenger compartment space. w Safety w Component built-in type frame · Thanks to a large crushable zone, collision impact is A rigid, hollow 15 cm frame structure was provided under uniformly dispersed throughout the vehicle body. the floor to house batteries, inverters and other main · Stronger grip on the road during turning and a lower components. This framework allows the center of gravity to be center of gravity lowered, and because the battery container is integrated into · Rigid body structure to withstand ultrahigh speeds the structure, the vehicle weight can be reduced and the space e High performance above the floor increased. · Maximum speed of 400 km/h achieved in 75 seconds e Tandem wheel type suspension (high-speed type) A suspension structure including two small wheels in place · Acceleration to 100 km/h in 4 seconds (high-acceleration of one large wheel and their shock absorbers connected to type) each other by an oil pipe was adopted. The increased ground · Long-distance driving, 320 km per charge (high- contact area intensifies grip on the ground, and the smaller acceleration type) wheels increase the vehicle room space. As the shock load Developed as part of this project were two types of from the road on one wheel is dispersed to the other as well, vehicles: a high-speed type (No. 1) and high-acceleration type drive comfort is improved. (No. 2). At the 37th Tokyo Motor Show in 2003, Keio University exhibited a model mock-up and a skeleton chassis In-wheel motor (Mounted in each wheel) Tandem wheel suspension model, which successfully publicized the existence of high- · Higher efficiency (Spring systems of two · Lighter weight wheels are connected by performance electric vehicles and the progress of this project. · Expanded effective hydraulic piping.) space · Improved drive comfort · Improved cornering performance · Expanded effective space

Component built-in frame (Batteries, inverters and controllers are mounted under floor.) · Expanded effective space · Lower center of gravity

Fig. 2 Core technology concept of Eliica

In order to impress the public with the running performance of electric vehicles, the design maximum speed was set at 400 km/h, and the vehicle body was designed to have sufficient space to accommodate four passengers. Also, for continuity with planned second-stage prototypes, the development aimed at achieving a vehicle to satisfy elements and functions for running on city streets to make it eligible for license plates. The name "Eliica" is an acronym of "Electric Lithium-Ion Battery Car," expressing a new-concept vehicle driven by a lithium-ion battery with environmental friendliness, safety, Fig. 3 Exhibition at Tokyo Motor Show and high performance.

36 Koyo Engineering Journal English Edition No.168E (2005) −Bearing & Seal Technologies for Electric Vehicle Eliica Project−

Table 1 Specifications of Eliica first stage prototypes2)

No. 1 (High-speed type) No. 2 (High-acceleration type) Total length 5 100 Total width 1 900 Total height 1 365 1 415 Dimensions, Wheel base 2 900 mm Tread, front 1 650 Tread, rear 1 580 Mini. height 80 130 Passenger capacity, persons 5 Vehicle weight, kg 2 400 Drive system Electric motor drive by secondary batteries Type Lithium-ion Battery Capacity, kWh 31 55 Voltage, V 332 328 Type Permanent magnet, synchronous type Max. torque, N·m 100 × 8 Max. output, kW 60 × 8 Max. speed, min−1 12 000 Motor Base speed, min−1 5 730 Inverter type PWM Dimensions, mm 300 (L) × 330 (W) × 150 (H) Weight, kg 17 Front Double wishbone with pull rod Suspension Rear Double wishbone Electric power assist Steering Steer 1/2/4 axles Brake 8 wheels regenerative disc brakes Designed max. speed, km/h 400 190 Designed max. acceleration, G 0.4 0.8 Performance Acceleration time from 0 to 400 m, s 15.3 11.3 Mileage/charge, km 200 320 Charging time, min (0 /70%) 4 30

3. Structure of In-Wheel Motor and Bearing/Seal shaft diameter was increased in order to cope with the Technologies increased input torque. As this dictated a very thin space for the seal, Koyo developed an ultrathin seal (25mm ID × 31mm The in-wheel motor for which Koyo provided bearing and OD) with high sealing capability. seal technologies is a unit integrating a motor, reduction gears, In both the No. 1 and No. 2 vehicles, special ball bearings a wheel bearing and a braking system. with Koyo's original heat treatment for improving bearing life The bearings and seals and their surrounding structures were used as sun gear support bearings in order to secure basically achieved the design targets and good actual durability in the allowable small space. performance in the KAZ project. For the Eliica No. 1 high- For the hub bearing, a first-generation double row angular speed type, however, at the maximum speed of 400 km/h the contact ball bearing was selected based on consideration of the −1 −1 planetary gear rotates at 13 000 min and orbits at 3 500 min , drive unit structure. The bearing was designed with a packing speeds which were judged to exceed the seizure limiting seal mounted to provide high rigidity and sufficient durability. speeds for the full complement needle roller bearings with oil To support the motor, a ball bearing with light-contact RD bath lubrication used in the KAZ. Therefore, a cage & roller type seals, which are widely used in motors, was selected. The type needle roller bearing was designed and manufactured bearing incorporated high-temperature seal material and based on Koyo's expertise. grease able to handle heat generation from the motor at high- For the No. 2 high-acceleration type vehicle, the output speed rotation.

Koyo Engineering Journal English Edition No.168E (2005) 37 −Bearing & Seal Technologies for Electric Vehicle Eliica Project−

The assembled in-wheel motor units were tested on a bench 4. Future of Eliica Project with a dynamo tester under torque loading simulating a vehicle speed of 400 km/h at rotational speeds of up to 12 000 In the future, there are plans to continue the Eliica project min−1 before mounting them on actual vehicles. by manufacturing several dozen second-stage prototypes by The bearings and seals disassembled after the dynamo test small-lot production and accumulate data during operational revealed no traces of abnormal temperature rise, seizure or testing. wear, verifying that Koyo's basic design and the selection of Koyo will continue to participate in the Eliica project and bearings were appropriate. other research projects that have the potential to contribute to society by creating new means of transportation while intensifying efforts to create technology useful in environmental conservation. Finally, the author expresses his sincere thanks to Professor Hirokazu Yoshida, Professor Hiroshi Shimizu and all other staff members of the Electric Vehicle Laboratory of Keio University and all other participating companies for the guidance and assistance they provided in order to enable Koyo to perform its responsibilities in this project.

References

1) Electric vehicle laboratory of Keio university "eliica.com" homepage. 2) Electric vehicle laboratory of Keio university: 37th Tokyo Motor Show press release.

Fig. 4 In-wheel motor

Fig. 5 In-wheel motor mounted on vehicle

Subsequently, the completed prototype vehicle was test- driven by former F1 driver Ukyo Katayama on a Japanese proving ground, followed by another test run at 370 km/h on the Nardo Proving Ground in Italy. In both of these tests, the bearings and seals remained completely good, and we are sure Koyo's core technology contributed to the success of this project.

Fig. 6 Eliica during road testing C. MUROTANI*

* Toubu Technical Center (bearing), Bearing Business Operations Headquarters

38 Koyo Engineering Journal English Edition No.168E (2005)